An SPI type fuel injection system is provided with only one fuel injection valve for supplying fuel to all cylinders of an internal combustion engine. Therefore, cost for manufacturing such a type of apparatus can be decreased when compared with a conventional fuel injection apparatus wherein a plurality of fuel injection valves are provided in respective cylinders of the engine. However, the SPI type of fuel injection apparatus suffers from a disadvantage in that a difference in the air-fuel ratio, the value of which difference is changed in accordance with the degree of the throttle opening, takes place between the cylinders. This is because the value of the difference between the amount of air passed through one side of the throttle valve and the amount of air passed through the other side of the throttle valve changes in accordance with the degree of the throttle opening, while the amount of the fuel passed through one side of the throttle valve is, irrespective of the throttle opening, equal to the amount of fuel passed through the other side of the throttle valve. Due to the difference in the air-fuel ratio, an idealized operation of the engine cannot be obtained.